Daptomycin is a lipopeptide antibiotic with activity against gram-positive organisms. Daptomycin is produced by fermentation of Strepromyces roseosporus and then purification of the fermentation broth. The mechanism of action for daptomycin is that it binds to bacterial membranes and causes a rapid depolarization of the membrane potential. This loss of membrane potential causes inhibition of protein, DNA and RNA synthesis, resulting in bacterial cell death. Daptomycin is approved for complicated skin and skin structure infections (cSSSI) and Staphylococcus aureus bloodstream infections (bacteraemia). Daptomycin is marketed by Cubist Pharmaceuticals under the trademark CUBICIN®.
Daptomycin was first described in the mid 1980's in several patents and journals; U.S. Pat. No. 4,537,717 and Debono M. et al, Journal of Antibiotics, 1986, Vol. XL, No 6, 761-777. Since then there have been several publications regarding improved fermentation processes and purification processes.
In U.S. Pat. No. 4,885,243 an improved fermentation process for making daptomycin is described. This method describes the feeding of decanoic fatty acid or ester or salts thereof to a fermentation broth of Strepromyces roseosporus. During fermentation, the decanoic fatty acid will be inserted to the molecule to form the decanoic side chain of daptomycin.
In the prior art, several purification processes for purifying daptomycin has been described. U.S. Pat. No. 4,874,843 describes a method for purifying daptomycin in which the fermentation broth was filtered and added to a chromatographic column containing Diaion® HP-20 styrene-divinylbenzene resin for hydrophobic compounds. After elution, the semipurified daptomycin was passed through a column containing Diaion® HP-20ss resin and then added to another column containing Diaion® HP-20 resin, a directly polymerized small particle size version of HP-20. In addition to these steps, attempts to increase the purity with several additional chromatographic steps without any success are described. The '843 patent further teach that by using a non-functional resin and an aqueous solution and including a step where water are physically removed and then rewet the resin with a polar organic solvent, the purity of the product is increased from 80% to 93%. This process is time consuming and not very well suitable for industrial production.
The U.S. RE 39,071 patent describes the two major impurities found in the production of daptomycin, the anhydro-daptomycin and the beta-isomer of daptomycin. The U.S. RE 39,071 further states that by using the method described in example 1-3 you will have a daptomycin product comprising less than 6% of the two mentioned impurities. Example 3 describes a method where intermediate quality of daptomycin is further purified in a method comprising four chromatographic steps and additional desalting, concentration and freeze drying steps. In the chromatographic steps acetonitrile is used for washing and elution and in addition you have to perform the method with chilled solutions and in a chilled room.
U.S. Pat. No. 6,696,412 patent disclose a method for purifying daptomycin by utilizing an anion exchange chromatography step where a modified buffer is used for elution and by utilizing a microfiltration step where daptomycin forms micelles. There are several methods described in this patent that is a combination of the two steps mentioned above in combination with other purification steps familiar to the person skilled in the art. The highly purified daptomycin product is defined in the patent to be daptomycin with a purity level of 95-97%.